Polyene motifs with (E,Z) stereochemistry are ubiquitous in biologically active and naturally occurring systems. See (a) McGarvey, B. D.; Attygalle, A. B.; Starratt, A. N.; Xiang, B.; Schroeder, F. C.; Brandle, J. E.; Meinwald, J. Nat. Prod. 2003, 66,1395. (b) Robinson, C. Y.; Waterhous, D. V.; Muccio, D. D.; Brouillette, W. J. Bioorg. Med. Chem. Lett., 1995, 5, 953. (c) Asfaw, N.; Storesund, H. J.; Skattebol, L.; Aasen A, J. Phytochemistry 1999, 52, 1491. (d) Hiraoka, H.; Mori, N.; Nishida, R.; Kuwahara, Y. Biosci. Biotechnol. Biochem., 2001, 65, 2749. (e) Matsumoto, H.; Asato, A. E.; Denny, M.; Baretz, B.; Yen, Y-P.; Tong, D.; Liu, R. S. H. Biochemistry, 1980, 19, 4589. Several natural compounds are shown below:

Accordingly, polyene motifs with (E, Z) stereochemistry represent synthetically important targets. See (a) Knowles, W. S. Angew. Chem., Int. Ed. 2002, 41, 1998. Noyori, R. Angew. Chem., Int. Ed. 2002, 41, 2008. (b) Sharpless, K. B. Angew. Chem., Int. Ed. 2002, 41, 2024. (c) Chauvin, Y. Angew. Chem., Int. Ed. 2006, 45, 3740. (d) Schrock, R. R. Angew. Chem., Int. Ed. 2006, 45, 374. (e) Grubbs, R. H. Angew. Chem., Int. Ed. 2006, 45, 3760. Not only are synthetic routes to Z-alkenes relatively limited but such traditional approaches to unsaturated conjugated Z-polyenes as Wittig and Homer-Wadsworth-Emmons reactions, cannot be used to directly deliver unsaturated aldehydes. See (a) Smith, A. B III, Beauchamp, T. J.; LaMarche, M. J.; Kaufman, M. D.; Qiu, Y.; Arimoto, H.; Jones, D. R.; Kobayashi, K. J. Am. Chem. Soc. 2000, 122, 8654. (b) Dong, D-J.; Li, H-H.; Tian, S-K. J. Am. Chem. Soc. 2010, 132, 5018. (c) Still, W. C.; Gennari, C. Tetrahedron Lett. 1983, 24, 4405. (d) Molander, G. A.; Dehmel, F. J. Am. Chem. Soc. 2004, 126, 10313. (e) Huang, Z.; Negishi, E-I. J. Am. Chem. Soc. 2007, 129, 14788. (f) Belardi, J. K.; Micalizio, G. C. J. Am. Chem. Soc. 2008, 130, 16870. (g) Lindlar, H.; Dubuis, R. Org Synth. 1966, 46, 89. (h) Randl, S.; Gessler, S.; Wakamatsu, H.; Blechert, S. Synlett 2001, 430. (i) Kang, B.; Kim, D-H.; Do, Y.; Chang, S. Org. Lett. 2003, 5, 3041. (j) Hansen, E. C.; Lee, D. Org. Lett. 2004, 6, 2035. (k) Kang, B.; Lee, J, M.; Kwak, J.; Lee, Y. S.; Chang, S. J. Org. Chem. 2004, 69, 7661. (l) Sashuk, V.; Samojlowicz, C.; Szadkowska, A.; Grela, K. Chem Commun. 2008, 2468. (m) Crowe, W. E.; Goldberg, D. R. J. Am. Chem. Soc. 1995, 117, 5162.
The traditional metal-free approaches to unsaturated conjugated Z-polyenes, which are relatively few such as Wittig and Hornder-Wadsworth-Emmons reactions, cannot be used to directly deliver unsaturated aldehydes. The metal-catalyzed cross-coupling of two sp2-hybridized reactants requires activating functionalities (e.g., organoboranes or organo-stannanes) which may be toxic, expensive and/or deleterious for the overall atom efficiency. Methods for the direct incorporation of the unsaturated α,β-carbonyl compounds with the Z-stereochemistry are limited. See (a) Maynard, D. F.; Okamura, W. H. J. Org. Chem. 1995, 60, 1763. (b) Duhamel, L.; Guillemont, J.; Poirier, J-M. Tetrahedron Lett. 1991, 32, 4495. (c) Cahard, D.; Duhamel, L.; Lecomte, S.; Poirier, J-M. Synlett 1998, 12, 1399. (d) Amos, R. A.; Katzenellenbogen, J. A. J. Org. Chem. 1978, 43, 555.
The metal-catalyzed Claisen rearrangement offers new mechanistic paths to this classic reaction and significantly expands its synthetic utility. See (a) Tejedor, D.; Méndez-Abt, G.; Cotos, L.; García-Tellado, F. Chem. Soc. Rev., 2013, 42, 458. Aluminium: (b)Bates, D. K.; Janes, M. W. J. Org. Chem. 1978, 43, 3856. (c) Majumdar, K. C.; Chattopadhyay, B. Synth. Commun. 2006, 36, 3125. (d) Majumdar, K. C.; Islam, R. J. Heterocycl. Chem. 2007, 44, 871. (e)Majumdar, K. C.; Islam, R. Can. J. Chem. 2006, 84, 1632. (f) Majumdar, K. C.; Bhattacharyya, T. Tetrahedron Lett. 2001, 42, 4231. (g) Majumdar, K. C.; Ghosh, M.; Jana, M.; Saha, D. Tetrahedron Lett. 2002, 43, 2111. (h) Majumdar, K. C.; Bandyopadhyay, A.; Biswas, A. Tetrahedron 2003, 59, 5289. Cu(II), Sn(IV), Ti(IV) and La(III): (i)Takanami, T.; Hayashi, M.; Suda, K. Tetrahedron Lett. 2005, 46, 2893. (j) Trost, B. M.; Schroeder, G. M. J. Am. Chem. Soc. 2000, 122, 3785. (k) Nakamura, S.; Ishihara, K.; Yamamoto, H. J. Am. Chem. Soc. 2000, 122, 8131. (l) Nasveschuk, C. G.; Rovis, T. Org. Lett. 2005, 7, 2173. (m) Nasveschuk, C. G.; Rovis, T. Angew. Chem., Int. Ed. 2005, 44, 3264. (n) Kaden, S.; Hiersemann, M. Synlett 2002, 1999. (o) Helmboldt, H.; Hiersemann, M. Tetrahedron 2003, 59, 4031. (p) Abraham, L.; Korner, M.; Hiersemann, M. Tetrahedron Lett. 2004, 45, 3647. (q) Sharghi, H.; Aghapour, G. J. Org. Chem. 2000, 65, 2813. (r) Bancel, S.; Cresson, P. C. R. Acad. Sci. Ser. C. 1970, 270, 2161. (s) Nonoshita, K.; Banno, H.; Maruoka, K.; Yamamoto, H. J. Am. Chem. Soc. 1990, 112, 316. (t) Sugiura, M.; Nakai, T. Chem. Lett. 1995, 697. (u)Akiyama, K.; Mikami, K. Tetrahedron Lett. 2004, 45, 7217. (v) Itami, K.; Yamazaki, D.; Yoshida, J. Org. Lett. 2003, 5, 2161. (w) Jamieson, A. G.; Sutherland, A. Org. Biomol. Chem. 2006, 4, 2932. (x)Swift, M. D.; Sutherland, A. Org. Biomol. Chem. 2006, 4, 3889. (y) Nakamura, I.; Bajracharya, G. B.; Yamamoto, Y. Chem. Lett. 2005, 34,174. (z) Sattelkau, T.; Eilbracht, P. Tetrahedron Lett. 1998, 39, 1905. (aa) Eilbracht, P.; Gersmeier, A.; Lennard, D.; Huber, T. Synthesis 1995, 330; (ab) Sattelkau, T.; Hollmann, C.; Eilbracht, P. Synlett 1996, 1221.(ac) Sattelkau, T.; Eilbracht, P. Tetrahedron Lett. 1998, 39, 9647.
When metals coordinate with π-bases, such as alkenes or alkynes, the first step of the rearrangement can be described as a 6-endo-dig cyclization that leads to a cyclic six-membered intermediate (See FIG. 1). Thus, this mode of rearrangement was termed “cyclization-mediated pathway”. See (a) Henry, P. M. Acc. Chem. Res. 1973, 16. (b) Henry, P. M. Adv. Organomet. Chem. 1975, 13, 363. (c) Overman, L. E. Angew. Chem. Int. Ed. Engl. 1984, 23, 579. On the other hand, Lewis acids, such as Cu+2, Al+3 and H+ initiate the so-called “cation-accelerated oxonia Claisen” rearrangement by coordinating with oxygen (See FIG. 1). See (a) Maruoka, K.; Saito, S.; Yamamoto, H. J. Am. Chem. Soc. 1995, 117, 1165. (b) Stevenson, J. W. S.; Bryson. Tetrahedron Lett. 1982, 23, 3143. (c) Takai, K.; Mori, I.; Oshima, K.; Nozaki, H. Bull. Chem. Soc. Jpn. 1984, 57, 446. (d) Takai, K.; Mori, I.; Oshima, K.; Nozaki, H. Tetrahedron 1984, 40, 4013. (e) Takai, K.; Mori, I.; Oshima, K.; Nozaki, H. Tetrahedron Lett. 1981,22, 3985.
Recently, we reported a mechanistic study of Au(I)-catalyzed propargyl Claisen and allenyl vinyl ether rearrangement, where Au(I), commonly considered as an alkynophilic Lewis acid, coordinates with the oxygen and directs the Claisen rearrangement through an oxonia path. See (a) Vidhani, D. V.; Cran, J. W.; Krafft, M. E.; Manoharan, M.; Alabugin, I. V. J. Org. Chem. 2013, 78, 2059. (b) Vidhani, D. V.; Cran, J. W.; Krafft, M. E.; Alabugin, I. V. Org. Biomol. Chem., 2013, 11, 1624. The barrier for the alternative cyclization-mediated pathway is 1.5 kcal/mol higher. Two important features of the calculated Au-catalyzed cyclization-mediated pathway includes: 1) lack of substituent effects and 2) selective stabilization of the TS for the Grob fragmentation of the six-membered intermediate by Au(I)-catalysts.
The latter effect lowers the barrier to the extent that this intermediate corresponds to a shallow inflection on the potential energy surface, so the overall process blends the characteristics of a stepwise and a concerted process. The nature of this unusual potential energy surface depends strongly on substrate-catalyst coordination and solvent, as illustrated by the successful trapping of the six-membered intermediate by nucleophilic attack of water in dioxane reported by the Toste group. See (a) Sherry, B. D.; Maus, L.; Laforteza, B. N.; Toste, D. J. Am. Chem. Soc. 2006, 128, 8132.